Myths and facts about Ka-Band. Below a list of topics about Ka-Band which have been compiled by a major satellite operator.
Higher frequencies provide higher throughput
There is nothing fundamental in a frequency band which supports higher throughput. The amount of data that a satellite can transmit is determined by the design of the satellite. Each frequency band has been allocated a specific bandwidth which can be used by satellite operators. The spectrum allocations are 500 MHz in C-band, 500-1000 MHz (depending on region) for Ku-band, and 1000 MHz in Ka–band.
Ka-band is more cost effective because of smaller antennas
Due to the higher frequency of Ka-band, it is assumed that antennas will be smaller than Ku-band because the same performance can be achieved with a smaller antenna. However higher frequencies also result in greater path loss from the antenna to the satellite. When analyzed it can be seen that this increase in path loss nullifies the increase in antenna performance. Therefore, Ka-band antennas will typically be no smaller than their Ku-band equivalent for similar performance.
Ka-band suffers from rain fade worse than C or Ku-band
Higher frequencies experience higher precipitation attenuation. That is why rainfade is higher in Ka-band than Ku-band, which in turn is higher than C-band. For example, the attenuation associated with a moderate rainfall in Ka-band is comparable to that of a heavy thunderstorm in Ku-band. What this means in practice is that the link availability of Ka-Band networks will be less than that for Ku or C-band in all but the most arid conditions.
Attenuation mitigating techniques can compensate Ka-band rainfade
Ku and Ka-band links can use uplink power control to help mitigate the attenuation caused by rainfade to the uplink signal. Uplink power control is a system that increases the power transmitted by the earth station towards the satellite when it detects that the signal is fading due to precipitation. The typical range of UPC systems is 10dB, some of the uplink rainfades in Ka-band could be up to 20dB so while UPC will help increase link availability, it
will not fully address Ka-band rain fades.
Adaptive coding and modulation (ACM) is a recent development which allows a carrier to change modulation and coding dynamically, according to receive site conditions, so that it can maintain a higher link availability. There is a limit to how much rain fade ACM can address and, as with UPC, it is unlikely to be able to fully compensate for Ka-band downlink rainfade.
Ka band concentrates more power on a small geographic area.
While it is true that many Ka-band satellite systems utilize a multi-spot design which focuses power into small geographic areas, this is not unique to Ka-band and could just as easily be replicated in any satellite band.
High throughput satellites are Ka-band satellites.
A high throughput satellite is one that uses significant frequency reuse techniques, such as multiple spot beams, to multiply the effective throughput capacity of a satellite. There is not a widely accepted definition of how much throughput a satellite needs to support in order to be called a high throughput satellite.
Some market research firms consider that high throughput satellites should support throughputs in the range of 3 to 10 Gbps. As mentioned above, high frequency re-use techniques can potentially be applied to any satellite band to achieve these throughput levels.
Ka band is the best solution for airlines.
Aircraft spend most of their time flying above the weather, so this automatically mitigates the majority of the attenuation experienced in Ka-band. However as most Ka-band satellites employ small spot beams, maintaining communication with the aircraft will require a complex communication system that keeps the aircraft connected while moving from
beam to beam.
As an aircraft traverses from beam to beam the antenna will be required to change frequency and/or polarization, receive new beam map and maintain the session. Additionally, although a slightly smaller antenna may be possible, the waveguide losses at Ka-band may necessitate mounting the transmit amplifier under the radome, rather than in the aircraft, making for a more challenging installation than a comparable Ku-band system.